That actually happened to me as well! I am also on Xbox One. I was streaming when it happened. I wish I had just let it count up to see what happened. Did you let it count past -5?
Here is a picture of it happening to me. I was already half way down when I noticed it was in the negatives. :/
http://i.imgur.com/XCIM6b0.jpg
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Unfortunately I don't remember if it did. If I remember correctly, once it reached -5 it actually sent me down to join my allies.